Computer case screws

Last updated
From left to right: a #6-32 UNC thumbscrew, a #6-32 UNC screw, an M3 screw and a self-tapping screw for case fans PC Screws.jpg
From left to right: a #6-32 UNC thumbscrew, a #6-32 UNC screw, an M3 screw and a self-tapping screw for case fans

Computer case screws are the hardware used to secure parts of a PC to the case. Although there are numerous manufacturers of computer cases, they have generally used three thread sizes. The Unified Thread Standard (UTS) originates from the United States, while the ISO metric screw thread is standardized worldwide. In turn, these thread standards define preferred size combinations that are based on generic units—some on the inch and others on the millimetre.


The #6-32 UNC screws are often found on 3.5" hard disk drives and the case's body to secure the covers. The M3 threaded holes are often found on 5.25" optical disc drives, 3.5" floppy drives, and 2.5" drives. Motherboards and other circuit boards often use a #6-32 UNC standoff. #4-40 UNC thumb screws are often found on the ends of DVI, VGA, serial and parallel connectors.

More modern cases from certain manufacturers (Dell, Gateway) and enthusiast cases will lack screws altogether, instead utilizing a tool-less design.

#6-32 UNC screw

The #6-32 UNC screw has a thread pitch of 1/32 in (0.031250 inches (0.7938 mm)). 6-32 computer screw with hexagonal head and Phillips drive.png
The #6-32 UNC screw has a thread pitch of 1/32 in (0.031250 inches (0.7938 mm)).

The #6-32 UNC is a UTS screw specifying a major thread diameter of #6 which is defined as 0.1380 inches (3.51 mm); and 32 tpi (threads per inch) which equates to a thread pitch of 0.031250 inches (0.7938 mm). The optional UNC specification indicates the standard coarse thread is used which is defined for #6 screws as 32 tpi rendering 'UNC' redundant, however it may be seen when other specifications such as plating or other treatments are also specified. It is by far the most common screw found inside computer cases. [1] It commonly appears in lengths of 3/16 in (0.1875 inches (4.76 mm)) and 1/4 in (0.25 inches (6.4 mm)) or less often 5/16 in (0.3125 inches (7.94 mm)). Non-standard metricized lengths such as 5 millimetres (0.20 in) are also sometimes encountered. Nearly every brand new computer case comes with a bag of these. They are commonly used for the following purposes, however there are many exceptions:

They are almost always provided with a #2 Phillips drive. Sometimes a Torx drive is used instead. Both Phillips and Torx patterns may also be combined with a slot for a flat-blade screwdriver. Usually they are provided with a 1/4 in (0.25 inches (6.4 mm)) flanged hex head. Non-standard metricized 5.5 millimetres (0.22 in) flanged hex heads can also be encountered. Also common are pan head screws - a low disk with a chamfered outer edge. Because they are used in places where high torque is not required and easy removal and replacement may be desirable (such as on the side panels of the PC case), they are frequently available as thumbscrews with larger, knurled heads that can be removed with one's fingers or tools.

M3 screw

The M3 screw (bottom) has a thread pitch of 0.5 millimetres (0.020 in), which is finer than the 0.031250 inches (0.7938 mm) pitch of a #6-32 UNC screw (top). M3 screw and 6-32 UTS screw with ruler thread pitch.png
The M3 screw (bottom) has a thread pitch of 0.5 millimetres (0.020 in), which is finer than the 0.031250 inches (0.7938 mm) pitch of a #6-32 UNC screw (top).

The M3 is a metric screw specifying a nominal diameter of 3 millimetres (0.12 in); and standard coarse thread pitch defined as 0.5 millimetres (0.020 in). The M3 is the second most common screw found in PCs. [1] It commonly appears in many lengths from 1 to 20 mm. Nearly every brand-new computer case comes with a bag of these. Notwithstanding many exceptions, they are commonly used for securing the following devices: [2] [ failed verification ]

M3 screws typically accept a #2 Phillips screwdriver tip.

Motherboard standoff

Various types of motherboard standoffs Toennchen IMGP5029 wp.jpg
Various types of motherboard standoffs

Most cases use threaded brass standoffs (Jack Screw Standoffs) for attaching the motherboard to the case chassis. Because the case material is usually a conductive metal, attaching the motherboard directly to it can cause a short circuit. Sometimes threaded or snap-lock plastic standoffs are used, which are less secure, but equally useful in a stationary computer. The standoff provides a margin of space between the motherboard and the case to keep the multiple solder points below from grounding and short-circuiting.

Usually, the standoff has a #6-32 UNC male thread on one end which screws into a threaded hole in the case or motherboard backplate and a #6-32 UNC female thread in the other end which accepts a screw to retain the motherboard. Less often, the standoff has a female thread in both ends and a second screw is used to attach it to the case. Some standoffs use the M3 female thread (which faces the motherboard) instead of #6-32 UNC, and on a rare occasion a mixture of types can be used in the same case.

All-metric standoffs are stated as threading x hex length x threaded length. For example, M3 x 10 x 6 means a standoff with M3 male and female threading, 10 mm hex length, and 6 mm threaded length. M6 x 10 x 8 means M6 male and female threading, 10 mm hex length, and 8 mm threaded length. Typically, M2.5 and M3 standoffs tighten with a 5 mm socket, M4 standoffs with a 6 mm socket, M5 standoffs with a 7 mm socket, and M6 standoffs with an 8 mm socket, but this is not always the case.

Version 2.1 of the ATX specification states that the length of standoffs needs to be at least 0.25 inches (6.4 mm), with their cross sections fitting within 0.40 by 0.40 inches (10 mm × 10 mm) square areas centered around each mounting hole on ATX motherboards. [3]

#4-40 UNC thumbscrews

Pairs of #4-40 UNC thumbscrews are used to fasten certain connectors to hardware ports. The screws are typically located on either side of D-subminiature connectors such as on VGA, serial, parallel and legacy game controller ports. They are also more recently used on DVI connectors. The typical length for a #4-40 screw used in PCs is 3/16 in (0.1875 inches (4.76 mm)). Occasionally the 4-40 hexagonal standoffs come loose when loosening the 4-40 screws to remove a cable, gender changer, or adapter. The 4-40 standoffs typically tighten with a 5 mm or 3/16-inch socket. Care should be taken not to overtighten them as they are somewhat delicate and will snap off at the base with excessive torque.


Steel is by far the most common material used, frequently with a plated or anodized finish. Other materials including brass, aluminum, nylon and various plastics are also used for applications with particular physical or aesthetic requirements.


The #6-32 UNC is a thicker screw with a more coarse thread. This makes it more suitable for fastening larger parts and thicker materials requiring increased holding strength. Its larger size and coarse thread make it easier to work with during assembly, with less risk of cross threading. The integrated flange provides greater holding strength with less risk of pull through. The hex head makes it easier to work with during assembly with powered torque screwdrivers.

The M3 is a thinner screw with a finer thread than the #6-32 UNC. This makes it more suitable for fastening into smaller parts and thinner materials requiring good strength in a limited space. Its size and fine thread make it appropriate for applications where a #6-32 UNC would be excessively bulky without providing any other benefits versus the smaller M3.


A regular computer case may require/include [4]

Related Research Articles

Motherboard Main printed circuit board (PCB) for a computing device

A motherboard is the main printed circuit board (PCB) in general-purpose computers and other expandable systems. It holds and allows communication between many of the crucial electronic components of a system, such as the central processing unit (CPU) and memory, and provides connectors for other peripherals. Unlike a backplane, a motherboard usually contains significant sub-systems, such as the central processor, the chipset's input/output and memory controllers, interface connectors, and other components integrated for general use.

ATX Motherboard and power supply configuration

ATX is a motherboard and power supply configuration specification developed by Intel in 1995 to improve on previous de facto standards like the AT design. It was the first major change in desktop computer enclosure, motherboard and power supply design in many years, improving standardization and interchangeability of parts. The specification defines the dimensions; the mounting points; the I/O panel; and the power and connector interfaces among a computer case, a motherboard, and a power supply.


Torx, developed in 1967 by Camcar Textron, is a trademarked type of screw drive characterized by a 6-point star-shaped pattern. A popular generic name for the drive is star, as in star screwdriver or star bits. The official generic name, standardized by the International Organization for Standardization as ISO 10664, is hexalobular internal. This is sometimes abbreviated in databases and catalogs as 6lobe. Torx Plus,Torx Paralobe and Torx ttap are improved head profiles.

Mini-ITX 17 × 17 cm motherboard

Mini-ITX is a 17 × 17 cm (6.7 × 6.7 in) motherboard form-factor, developed by VIA Technologies in 2001. They are commonly used in small-configured computer systems. Originally, they were a niche product, designed for fan-less cooling with a low power consumption architecture, which made them useful for home theater PC systems, where fan noise can detract from the cinema experience. The four mounting holes in a Mini-ITX board line up with four of the holes in ATX-specification motherboards, and the locations of the backplate and expansion slot are the same. Mini-ITX boards can therefore often be used in cases designed for ATX, micro-ATX and other ATX variants if desired.

AT (form factor)

In the era of IBM compatible personal computers, the AT form factor referred to the dimensions and layout of the motherboard for the IBM AT. Like the IBM PC and IBM XT models before it, many third-party manufacturers produced motherboards compatible with the IBM AT form factor, allowing end users to upgrade their computers for faster processors. The IBM AT became a widely copied design in the booming home computer market of the 1980s. IBM clones made at the time began using AT compatible designs, contributing to its popularity. In the 1990s many computers still used AT and its variants. Since 1997, the AT form factor has been largely supplanted by ATX.

Computer case Enclosure that contains most of the components of a computer

A computer case, also known as a computer chassis, tower, system unit, or cabinet, is the enclosure that contains most of the components of a personal computer.

Socket wrench

A socket wrench is a type of wrench that inserts into a socket to turn a fastener, typically in the form of a nut or bolt.

Machine taper

A machine taper is a system for securing cutting tools or toolholders in the spindle of a machine tool or power tool. A male member of conical form fits into the female socket, which has a matching taper of equal angle.

Spacers and standoffs threaded separator of defined length used to raise one assembly above another

In general, a spacer is a solid material used to separate two parts in an assembly. Spacers can vary in size from microns to centimeters. They can be made of metal, plastic, glass, and other materials. Shapes include flat sheet, cylindrical and spherical.


microATX is a standard for motherboards that was introduced in December 1997. The maximum size of a microATX motherboard is 9.6 × 9.6 in (244 × 244 mm). The standard ATX size is 25% longer, at 12 × 9.6 in (305 × 244 mm).

The shank is the end of a drill bit grasped by the chuck of a drill. The cutting edges of the drill bit contact the workpiece, and are connected via the shaft with the shank, which fits into the chuck. In many cases a general-purpose arrangement is used, such as a bit with cylindrical shaft and shank in a three-jaw chuck which grips a cylindrical shank tightly. Different shank and chuck combination can deliver improved performance, such as allowing higher torque, greater centering accuracy, or moving the bit independently of the chuck, with a hammer action.

Tripod (photography)

In photography, a tripod is used to stabilize and elevate a camera, a flash unit, or other photographic equipment. All photographic tripods have three legs and a mounting head to couple with a camera. The mounting head usually includes a thumbscrew that mates to a female threaded receptacle on the camera, as well as a mechanism to be able to rotate and tilt the camera when it is mounted on the tripod. Tripod legs are usually made to telescope, in order to save space when not in use. Tripods are usually made from aluminum, carbon fiber, steel, wood or plastic.

British Standard Whitworth (BSW) is an imperial-unit-based screw thread standard, based on the Whitworth thread devised and specified by Joseph Whitworth in 1841, which was the world's first national screw thread standard,

Molex connector

Molex connector is the vernacular term for a two-piece pin and socket interconnection. Pioneered by Molex Connector Company, the two-piece design became an early electronic standard. Molex developed and patented the first examples of this connector style in the late 1950s and early 1960s. First used in home appliances, other industries soon began designing it into their products from automobiles to vending machines to mini-computers.

Sex bolt

A sex bolt,, is a type of fastener (nut) that has a barrel-shaped flange and protruding boss that is internally threaded. The boss sits within the components being fastened, the flange provides the bearing surface. The sex bolt and accompanying machine screw sit flush on either side of the surfaces being fastened. It is normally chosen because of its low profile compared to other nuts. The sex bolt often has a built-in feature, such as a slot, to aid in tightening the fastener. Some sex bolts, more commonly known as "architectural bolts", have knurled barrels to allow one-sided assembly. "Binding posts" are similar to architectural bolts in that they are designed to be assembled from one side, but they have teeth on the flanged surface to keep them fixed.

The ISO metric screw thread is the most commonly used type of general-purpose screw thread worldwide. They were one of the first international standards agreed when the International Organization for Standardization (ISO) was set up in 1947.

Screw Type of fastener characterized by a thread wrapped around a cylinder core

A screw and a bolt are similar types of fastener typically made of metal, and characterized by a helical ridge, known as a male thread. Screws and bolts are used to fasten materials by the engagement of the screw thread with a similar female thread in the matching part.

Hex key Hand tool for certain types of screws

A hex key or Allen key, is a simple tool used to drive bolts and screws with hexagonal sockets in their heads.

M-LOK Type of Attachment System

M-LOK, standing for Modular Lock, is a free licensed firearm rail interface system developed and patented by Magpul Industries.


  1. 1 2 Rutter, Daniel Dan's Data - Letters 53, "Screwed", 2006-02-26
  2. "2.5-inch Hard Disk Drives Installation Guide" (PDF). HGST. January 30, 2007. Archived from the original (PDF) on December 24, 2012. Retrieved November 16, 2014.
  3. "ATX Specification, Version 2.1: Section 3.4.2 Secondary (Bottom/Solder) Side Height Constraints" (PDF). 2012-08-18. p. 18. Archived from the original (PDF) on 2016-08-17. Retrieved 2014-12-22.
  4. "H440 Manual" (PDF). Nzxt . Retrieved 2017-02-07.